This propulsion system uses two nested tubes (I usually use 1.5” and 2” PVC) of no particular size, duct tape, cardboard, and yarn to produce a large low pressure blast of air. With long ( 3’ ish) airgun-fit barrel material it vacuum loads and fires well, regardless of how many darts you put in the barrel. I've been making them for about a year and a half, found the internet nerf community about 6 months ago, and feel its about time I did a writeup. I did a dick-waving video earlier that features some HAMP guns here:

1. Cut the 2” PVC to length X+2, where X = stroke. I use about 12” normally.
2. Cut the 1.5” PVC to length X+4”, or X + whatever amount of PVC you want to use as a handle, or attach a handle/linkage.

3. Cap the 2” PVC however you want, but a cardboard cover/duct tape cover (See #5) will be easier to work with later than the regular endcap if you want to maximize stroke/minimize deadspace.

4. Cap the 1.5” PVC with something that easily clears the entrance to the 2” PVC. Standard endcaps will not work, so I recommend the cardboard/duct tape cover (See #5).

5. Duct Tape / Cardboard End Caps:
a. Cut out a circle of cardboard for both the inner and outer diameter of the tube you want to seal. Go slightly undersize for the inner. (Exact size could work if you are perfect in 5b.
b. Attach the inner (small) circle close to the center of the outer (large) circle. Glue is good here, since you don’t want to affect the diameter of the circle by taping over it. But, you CAN just use a mini-loop of duct tape.
c. Put the cardboard on the end of the tube. If you have a voluminous glue, like elmers, wood glue, or gorilla glue, its very handy here--Put it on the inside corner between the small and large circle, and you won’t have to worry about seal in 5d and 5e. The glue isn’t for strength.
d. Put thin (<1/2”) strips of duct tape tightly over the cap. If you did not use glue in 5c, you need to get something close to a seal here—Do this by going in a spiral, with each strip overlapping the previous, until have covered the endcap (180 degrees).
e. To complete the seal, and keep the end cap from peeling off, place a final strip of duct tape around the perimeter of the endcap / PVC interface, on top of the existing strips of duct tape. Thicker strips of duct tape will make it stronger, but I’ve done fine with ½”. Make sure that this tape extends slightly past the end of the cylinder. More winds adds strength, but if this is a inner/plunger cylinder, you probably only have room for a couple turns.
f. Cut and remove the duct taps strip ends sticking out past the ring of duct tape. A steak knife works extremely well for this, and other cardboard/duct tape/mixed material cutting jobs. I recommend keeping one in your crafting arsenal, since you don’t want to switch between using the knife for duct tap and using the knife for steak.

This post has been edited by KaneTheMediocre: 09 February 2015 - 08:58 PM

6. Squishy Slippery Seal: There are a many ways to do this. I started by taping down a strip of foam around the end of the tube, where the tape would be on each side of the foam, tight enough to compress it to a smaller diameter than the foam between the tape. Later I used old socks by cutting rings out of the ankle, and using them like the foam strip. Later simply stretched a sock over the end of the plunger (high friction), and even used shamwow fabric at one point. My current kick is the yarn spiral, which I think is best because it is easy and adjustable.
a. Tape down one end of the yarn, at the end of the 1.5” PVC. Wind a few layers of duct tape to make a retaining ring for the yarn.
b. Wind the yarn around the tube in a spiral-More winds and more distance covered by the yarn will result in a better seal, but they reduce the available stroke, because you don’t want the plunger partly out of the tube (see 7).
c. Tape the other end down, and make a few winds of tape for a retaining ring.
7. When you wind the yarn, you can make tighter winds for a more rigid, smaller OD, and lower stiction seal—But, with tighter winds, there is less “squishiness”, and thus less room for error on the outer diameter. For a larger OD, you can make a few winds of tape beneath the whole yarn assembly,
or you can wind more loosely. Neither good seal nor particularly low friction are required for this to work, but improving these will be beneficial. Using duct tape beneath the yarn becomes absolutely necessary when you have a wide gap to fill between the inner and outer tubes of the HAMP, as illustrated here:

You can't see it in these pics, but there are actually 2 yarn/duct tape seals, spaced about 3" apart, to help keep inner and outer tubes of the MegaHamp coaxial. In order to get the seal/slip that you want, you may have to tighten/loosen the yarn after you've put it together--fortunately, this only requires undoing the last strip of duct tape on the plunger. However, if you decide you want more duct tape beneath the yarn, you pretty much have to start over.

8. HAMP systems work well with long, loose fitting barrels. With tagger darts, which have been my primary ammo for these, I have had the best luck with ½” EMT steel electrical conduit, which was $1.35 / 10 feet at home depot. ½” PVC will also work, and in fact gets slightly better range, but it occasionally jams. In general, any material used as an “air gun” fit will work well--the EMT, despite a 5/8" OD, will fire streamlines from a HAMP, albeit poorly. So yeah, loose dart fit is good.

Questions are welcome, even stupid questions. Which is not to say I won't mock you if you ask a stupid question, but I welcome the opportunity nonetheless. Any details you feel are missing may help me improve this writeup.

We (mostly Kane) built this HAMP a few weeks ago in the cancer shack. It's incredible how much air this system puts out. Most of the modifications and stuff I do involve, relatively low volume, high pressure. This is way cooler. With mad airflow you don't need perfect seal by any means. Plus they don't need a trigger to fire.

But seriously, you need to post a picture of the dual action mega-super HAMP. Now that is a scary weapon.

This post has been edited by Ryan201821: 24 February 2010 - 11:32 PM

VACC, on 13 May 2011 - 07:30 AM, said:

Consider it a bottled universe under the magnanimous control of Ryan McNumbers. Trying to redefine the foundation of said universe will ultimately result in the cessation of your existence within it.

Wow, now what I would like to know is if it's possible to make one for a ball gun. Homemade Reactor anyone?

And Ryan if you think this is cool, you need to get your hands on an Expand A Blast.

This is definitely capable of launching a ball pretty far, or at least better than most ball guns. I'm going to build my version tomorrow and I'll test it out with a ball barrel attachment on it.

EaBs have maybe 1/10th of the volume as the Mega HAMP we built. Look at the picture I posted. There is at least three feet of 1/2" PVC that is just dead space. And it still penetrates cardboard. Fuck EaBs. They are insignificant compared to the volume this puts out.

Quote

The last gun in the video was simply awesome. Is there any chance of a writeup for that?

Yo, this is the write-up.

VACC, on 13 May 2011 - 07:30 AM, said:

Consider it a bottled universe under the magnanimous control of Ryan McNumbers. Trying to redefine the foundation of said universe will ultimately result in the cessation of your existence within it.

If one would not have the materials to do this, would you be willing to sell one of your one? And for how much?Please answer.

"- 99% of teens would cry if they saw Justin Beiber standing on top of a sky scraper, about to jump. If you're one of the 1% who would sit there eating pop corn screaming "DO A FLIP YOU FAGGOT!" Post this as your sig."

If one would not have the materials to do this, would you be willing to sell one of your one? And for how much?Please answer.

It's fucking duct tape, PVC, cardboard, and yarn. The cuts are made with a combination of hacksaw, scissors, and steak knife. We're not milling military grade aluminum on a CNC machine here.

"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
Kruger and Dunning (1999)

I got to see these at Chano 3, and they stand proudly against the rape guns and +bows. It makes for a different style of play, but damn, I got hit by that thing alot..

Nice Kane, I was always curious as to what the seal was made out of. Using yarn means that you don't need lubricant, and thus, there is practically no maintenance unless you get something in the plunger. Thats an incredible idea.

My new favorite propulsion system, yo. I built a MEGAHAMP this weekend with outstanding results. My hamp accepts any kind of attachment. The best is definitely hopper clip on a hose. It's the perfect Nerf machine gun.

I know people also wanted to see it shoot with balls. I did experiment. I used a 2" PVC wye for the hopper. There is no actual barrel. The balls are pushed out of the lip on the front of the wye. I added a 2" x 1.5" reducer to create the lip for the balls. Then I added a seat for the balls so they don't get stuck behind the lip. The only problem is that one balls sometimes goes into the back of the hopper clip, and never fires.

Maybe I should put on an actual barrel. The only problem is PVC pipe doesn't have an ideal fit with the balls. 1.5" is too tight, and 2" is too loose. I'll have to experiment with some pipes that actually have nominal sizing and see if I can create the fit I need.

Right now, it shoots roughly 50' with the ball hopper clip. I believe it should be able to shoot a bit further. I'm open to ideas.

EDIT: Grammatical error.

This post has been edited by Ryan201821: 27 February 2010 - 02:43 PM

VACC, on 13 May 2011 - 07:30 AM, said:

Consider it a bottled universe under the magnanimous control of Ryan McNumbers. Trying to redefine the foundation of said universe will ultimately result in the cessation of your existence within it.